Compacting step by step

ABSTRACT

Method of producing a continuous length of product by passing a composition consisting of small particles and a binding agent through an open ended mold and compacting it step by step by lateral pressure. The mold for use in the method is longitudinally divided into at least four segments and of polyhedral internal cross-section, the segments being movable synchronously inwards and outwards transversely to the axis of the mold and being shaped to provide in the axial direction firstly a mold cavity tapering in the direction and then a cavity with walls parallel with the axis.

United States Patent [1 1 Onder COMPACTING STEP BY STEP [75} Inventor:Harald Onder,Wetzikon,

Switzerland [73] Assignee: Swiss Aluminium Ltd., Chippis Switzerland 221Filed: June 13,1972

2| App]. No.: 262,247

[56] References Cited UNITED STATES PATENTS 2.289.787 7/1942 Kaschke264/323 X an] 3,876,744 Apr. 8, 1975 2.708.770 5/1955 Hirres 264/l20 X2.844345 7/I958 Krall 264/l20 X 2.902.7l4 9/1959 Johnson 425/793.674.389 7/1972 Sturgeon 425/224 X Primary Examiner-Donald 1. ArnoldAssistant E.raminer-Thomas P. Pavelko Attorney Agent, or FirmErnest F.Marmorek [57] ABSTRACT 3 Claims, [2 Drawing Figures PATENTEB APR 81975SHEET 2 [if 2 Fig.12

Fig.11

COMPACTING STEP BY STEP BACKGROUND OF THE INVENTION My present inventionrelates to the continuous production of a continuous length of productby compacting a composition consisting of small particles (that isgranular or composed of short fibres) and a binding agent. In the fieldof refractory and related materials such moldings, which must satisfyhigh requirements, are molded with a minimum possible addition ofbinding agent or plasticiser in block presses. The addition of bindingagent or plasticiser must be kept low so that no shrinkages or stressesoccur in the subsequent firing. The block presses have the disadvantagethat they work discontinuously. In the case of molding by extruders ahigher addition of binding agent or plasticiser is necessary, so thatthe moldings obtained cannot satisfy any high requirements after firing.

These considerations are valid both in the production of hightemperature-resistant bricks, for example from quartz sand, fireclay oraluminum oxide, and in the manufacture of artifical carbon and graphitemoldings.

In the production of aluminum by,electrolysis of aluminum oxide in afused fluoride bath, for example, artificial carbonaceous blocks areused as electrodes, for the production of which two main methods areknown.

According to one main method the green artificial carbonaceouscomposition is pressed in a mold with the aid of a plunger or of twooppositely acting plungers (block pressing). The method offers theadvantage that it is possible to work with a low addition of bindingagent. However it has two disadvantages. Firstly it is not continuousand therefore does not fit well into the course of processing. Secondlythe finished blocks have a very great anisotropy. which is attributableto the long compression distances. An inhomogeneous resistance of thefired (baked) electrodes against oxidiation results from the anisotropy.

According to the second main method the green artificial carbonaceouscomposition is processed in an extruder. The method is continuous andcan be fitted well into the course of processing, but it is veryexpensive as regards the machines used and the composition requiressubstantially more binding agent than in block pressing. Furtherdisadvantages derive from the very distinct radial anisotropy of theartificial carbonaceous blocks obtained. On the other hand theuniformity of the material quality over the length is advantageous.

The obtained artificial carbonaceous blocks are of course intendedsubsequently to be fired (baked).

SUMMARY OF THE INVENTION The object of my invention is the combinationof the advantages of both the main methods. that is block pressing andextrusion.

In accordance with my invention in a method of continuously producing acontinuous length of product by compacting a composition consisting ofsmall particles and a binding agent, the composition is introducedcontinuously into one end of an open ended mold and in passing throughthe mold, the composition is compacted step by step into a continuouslength by lateral pressure.

This method, which is particularly applicable to the production ofartificial carbonaceous products, is continuous and the requirement ofbinding agent or plasticiser is just as low as in the case of theconventional block pressing.

The composition is expediently introduced into a lon gitudinally dividedmold the segments of which, in the axial direction of passage of thecomposition, firstly form a tapering mold cavity and then a cavity withwalls parallel with the axis, the segments moving synchronously back andforth perpendicularly to the axis of the mold to produce the step bystep compaction. At every movement of the mold segments apart thecomposition is moved forwards and at every movement together it isfurther compacted.

The composition is most advantageously introduced into the wider end ofthe mold by means of a worm screw feeder which is arranged axially ofthe mold. The filling pressure thus achieved is intended both to preventthe development of a force component in the direction against thematerial flow through the mold, so that the cross-sections in thecontinuous length remain even, and to effect the opening of the mold andthus the longitudinal movement of the continuous length.

The invention also includes a mold for use in the method, the mold beingopen ended and longitudinally divided into at least four segments and ofpolyhedral internal cross'section, the segments being movablesynchronously inwards and outwards transversely to the axis of the moldand being shaped to provide in the axial direction firstly a mold cavitytapering in the direction and then a cavity with walls parallel with theaxis.

Preferably, the segments each provide one side of the polyhedron and aresymmetrically arranged around the axis of the mold and abut one anotheracross planes which are continuations of the sides of the polyhedron,the segments being movable linearly in guides substantially tangentiallyof the polyhedron.

A machine for carrying out the method will consist of such a moldtogether with a device for introducing the composition into the widerend of the mold.

DESCRIPTION OF THE DRAWINGS A machine for carrying out the method isillustrated by way of example in the accompanying drawings, in which:

FIGS. 1 to 6 are vertical axial sections ofa mold illustratingdiagrammatically the steps in producing a continuous length of productfrom green synthetic carbon;

FIGS. 7 to 10 illustrate a mold having four segments; and

FIGS. 11 and 12 illustrate a mold having six segments.

FIG. 1 shows the first phase in the commencement of operation. A mold 10with its segments 11 is open and filled with green articicialcarbonaceous composition 12. The mold has a tapering zone 13 and a zone14 with walls parallel with the axis. The vertical arrow 15 indicatesthe axial filling pressure. The mold 10 is closed at the bottom by afloor 16 for starting operation. At this stage the green artificialcarbonaceous composition has the same density in the entire mold cavity.

FIG. 2 shows the condition after the first compacting operation. Themold 10 has closed. The horizontal arrows 17 indicate the direction ofmovement of the mold segments. Compacting is indicated by thecrosshatching. The filling pressure 15, provided for example by a feedscrew, has prevented material from moving back upwards.

FIG. 3 shows the condition after the re-opening of the mold 10, that isto say after the mold segments ll have moved apart again (arrows 18).The floor 16 has been removed. The compacted composition has been moveddownwards by the filling pressure 15 until the pressing rests upon thewalls of the tapering mold cavity l3. Refilling has then been effectedwith further uncompacted artificial carbonaceous composition 12.

In FIG. 4 the mold is closed again. The second compacting operation hastaken place. Here again the filling pressure has prevented material frommoving back upwards. The twice-compacted artificial carbon compositionis indicated by the cross-hatching and an additional horizontalhatching. The part 19 of the car bonaceous body which has emerged fromthe mold is only cross-hatched. lt has been subjected to only one singlecompacting operation, and is waste from starting up operation.

ln FIG. 5 the mold 10 has opened again and the artificial carbonaceousbody has been moved downwards a second time by the filling pressure 15.A further quantity of uncompacted artificial carbonaceous composition 12has been added.

FIG. 6 shows the condition after the third closure of the mold 10. Thethrice-compacted composition is indicated by cross-hatching andadditionally by horizontal and vertical hatching. in the case of thesize ratios as sketched in the Figures this would be the usable finalstate of compacting; in this case only the lowermost part 19 of thecarbonaceous body and the next following part 20 would be waste fromstarting operation.

The tool can have different dimensions and can achieve a finalcompacting for example only after closure of the mold five or six timesor still more frequent closure, in which case that length of thecarbonaceous body which comprises the insufficiently pressed parts is tobe regarded as waste from starting operation.

The distinctive feature of the method as described with reference toFIGS. 1 to 6 consists in that the main proportion of the compacting isdetermined not by the magnitude of the tool movement but by thegeometrical formation of the pressing tool (mold) itself. Thus it ispossible to keep the amplitude of the mold movement small andcorrespondingly to increase the frequency of the reciprocating movementof the mold segments, so that finally one can speak of a vibratingmovement. During the course of work a pressure gradient establishesitself in the mold which is dependent directly upon the geometrical formof the tool and the compression curve (density/pressure function) of theartificial carbonaceous mixture.

HO 7 indicates the performance capacity of such an apparatus. a is theangle of inclination of the walls of the tapering part of the moldcavity, A is the amplitude of the horizontal reciprocating movement andH the axial movement of the carbon length (feed movement) at everyopening of the mold. H corresponds to the value A/tana By way of examplethe following values are assumed:

f (frequency of horizontal movement) 10 Hz A 0.5 mm. H 5.7 mm. 17(efiiciency in relation to H) 50%.

On account of the adhesion friction of the artificial carbonaceouscomposition on the mold wall, an efficiency of only 50% is assumed. Thisproduces an actual axial movement H' of the artificial carbonaceouslength of H X 1 2.85 mm. per oscillation (horizontal movement back andforth). In an operation with a frequency off 10 Hz, the artificialcarbonaceous continuous length produced a length L is obtained which isequal to 2.85 l0 3600 102.6 in. per hour. With a final cross-section of500 X 500 mm. and an apparent density of L6 tons per cu. m. this wouldcorrespond to an hourly output of 4| .04 tons.

ln the example given the feed movement H per oscillation is relativelysmall. In order to achieve a composition compacting in the ration 2 lthe tapering part of the mold must have a length of about 1.200 mm. inthe case of an artificial carbonaceous final cross-section of 500 X 500mm. This has the result that the artificial carbonaceous composition hasreached its final density of 1.6 t/cu.m. only after about 400oscillations, and consequently that the length of waste from startingoperation amounts to about 1.200 mm. plus the length of the mold part ofconstant cross-section (for example 250 mm.

The most various artificial carbonaceous mixtures can be processed bythe method according to the invention. An artificial carbonaceousmixture for the manufacture of anodes for aluminum fusion electrolysishas for example the following composition by weight:

Petroleum coke grain size: 3.36 to 8.0 mm. l6.6% 1.68 to 3.36 mm. 12.5%

0.84 to L68 mm. 12.5%

0.42 to 0.84 mm. 8.3%

0.2l to 0.42 mm. 8.3%

0.2l mm. 24.8%

Coal tar medium-hard pitch (binding agent) 17.0%

In the processing of the green artificial carbonaceous compositionaccording to the method in accordance with the invention (as also inblock pressing and extruding) the binding agent must be plastic andtherefore the entire composition must be warm. For this reason thecomposition is brought before processing to a temperature which isdetermined by the viscositytemperature function of the binding agent. Inthe case of coal tar medium-hard pitch the requisite temperature liesbetween l25 and C. The composition is introduced into the mold at such atemperature. it is advisable to keep the temperature of the moldapproximately at the level of that of the introduced composition duringoperation.

In the production of the artificial carbonaceous com position in placeof petroleum coke as dry material there can of course also be consideredpitch coke or anthracite (the latter for the cathodes of aluminumelectrolysis cells) and in place of coal tar medium-hard pitch any othercokable binding agent (such as petroleum pitch) may be considered. Thedry material consists of amorphous carbon with a minimum of inorganicimpurities (10% in the case of anthracite, 0.5% in the case of pitch orpetroleum coke).

The mold of the illustrated machine has a polyhedral internalcross-section with at least four corners. lt consists for example ofsteel.

FIG. 8 shows a diagrammatic plan view of a mold 10 with four segments 11which are tapered at 13 and have a constant cross-section with parallelwalls at 14, namely in the open position, that is with segments drawnapart. The arrows 17 indicate the direction for the closing movement ofthe segments 11. The frame 21 contains the guides 22 for the movement ofthe segments 11 and takes up the deformation forces.

FIG. 9 shows diagrammatically the mold l0 with its segments 11 in theclosed position. 23 indicates the free cross-section which the lowerpart of the mold 10 (the part with parallel walls) then has and thusdetermines the cross-section of the continuous length to be produced.The arrows 18 indicate the direction for the movement of the segments 11apart.

FIG. 10 shows in perspective, partially in dot-anddash lines, one halfof the mold of FIGS. 8 and 9, the frame 21 being omitted.

FIG. 11 shows diagrammatically in plan view a mold 24 with six segments25 in the open position and FIG. 12 shows the same in the closedposition. In perspective the segments appear approximately like those ofFIG. l0. Each has a tapering part 26 and a part 27 which extendsparallel with the axis of the mold on the mold cavity side and thus withthe other segments produces a mold cavity having walls parallel with theaxis. 28 designates the frame.

What I claim is:

l. A method of continually producing, along an upright mold axis, acontinuous length of product by repeatedly compacting a compositioncomprising small particles and a in an open ended mold having an inletand outlet communicating with the mold cavity, said mold comprising aplurality of at least four segments disposed along said axis anddefining said cavity, said cavity having an inwardly tapered portion ina direction from the inlet to the outlet and having a straight axialportion in the vicinity of the outlet, each individual compactingcomprising the steps of:

moving all of the segments perpendicularly of, and

synchronously, towards said axis while preventing the development of aforce component in the direction against the material flow through themold whereby the composition in the cavity is compacted from more thantwo lateral directions to form said product; and

subsequently moving all of said segments away from said axis through afirst predetermined distance whereby said product will, with additionalcomposition introduced through said inlet into said wall cavity, bemoved towards said outlet through a second predetermined distance.

2. A method, as claimed in claim 1 further comprising introducing thecomposition into said inlet by means of a worm screw feeder with afilling pressure sufficient to overcome any force opposing the materialflow through the mold thereby restraining material from moving againstthe flow direction, and

to effect the opening of the mold and thereby the longitudinal advanceof the product for one feeding step.

3. A method according to claim I, in which the composition is a greenartificial carbonaceous composition. a 4: :r =1:

1. A METHOD OF CONTINUALLY PRODUCING, ALONG AN UPRIGHT MOLD AXIS, ACONTINUOUS LENGTH OF PRODUCT BY REPEATEDLY COMPACTING A COMPOSITIONCOMPRISING SMALL PARTICLES AND A IN AN OPEN ENDED MOLD HAVING AN INLETAND OUTLET COMMUNICATING WITH THE MOLD CAVITY, AND MOLD COMPRISING APLURALITY OF AT LEAST FOUR SEGMENTS DISPOSED ALONG SAID AXIS ANDDEFINING SAID CAVITY, SAID CAVITY HAVING AN INWARDLY TAPERED PORTION INA DIRECTION FROM THE INLET TO THE OUTLET AND HAVING A STRAIGHT AXIALPORTION IN THE VICINITY OF THE OUTLET, EACH INDIVIDUAL COMPACTINGCOMPRISING THE STEPS OF: MOVING ALL OF THE SEGMENTS PERPENDICULARLY OF,AND SYNCHRONOUSLY, TOWARDS SAID AXIS WHILE PREVENTING THE DEVELOPMENT OFA FORCE COMPONENT IN THE DIRECTION AGANIST THE MATERIAL FLOE THROUGH THEMOLD WHEREBY THE COMPOSITION IN THE CAVITY IS COMPACTED FROM MORE THANTWO LATERAL DIRECTIONS TO FORM SAID PRODUCT; AND SUBSEQUENTLY MOVING ALLOF SAID SEGMENTS AWAY FROM SAID AXIS THROUGH A FIRST PREDETERMINEDDISTANCE WHEREBY SAID PRODUCT WILL, WITH ADDITIONAL COMPOSITIONINTRODUCED THROUGH SAID INLET INTO SAID WALL CAVITY, BE MOVED TOWARDSSAID OUTLET THROUGH A SECOND PREDETERMINED DISTANCE.
 2. A method, asclaimed in claim 1 further comprising introducing the composition intosaid inlet by means of a worm screw feeder with a filling pressuresufficient to overcome any force opposing the material flow through themold thereby restraining material from moving against the flowdirection, and to effect the opening of the mold and thereby thelongitudinal advance of the product for one feeding step.
 3. A methodaccording to claim 1, in which the composition is a green artificialcarbonaceous composition.